1. Field of the Invention
This invention relates generally to a modular adhesive bead dispenser, and in particular, to a modular adhesive bead dispenser that is capable of dispensing fast curing adhesives without the nozzles becoming obstructed with hardened adhesive.
2. Discussion of the Prior Art
Numerous applications require the deposition of one or more adhesive beads onto a substrate such as used in the manufacturing of disposable diapers, sanitary napkins, and in preformed structural panel assemblies. There exists a variety of applicators for adhesive, including hand held and machine mounted that are capable of depositing both singular and multiple beads. Some of these adhesive applicators use air to assist in spraying the adhesive, such as is disclosed in U.S. Pat. No. 4,891,249. Also techniques have been developed for varying the shape of the bead such as a spiral deposition as found in U.S. Pat. Nos. 4,949,668 and 4,983,109.
Also, blowing dies have been developed such as disclosed in U.S. Pat. No. 5,145,689, which are particularly designed for hot melt adhesives. Some adhesive applicators use intermittently operated or air assisted dies. Melt blown applicators provide a generally uniform covering with a predetermined adhesive width to be deposited on a substrate, but do not have precise edge control, which is needed in some applications. Spiral nozzles on the other hand, deposit a controlled spiral bead on the substrate to provide good edge control but lack uniform coverage of the substrate. Also, in order to have more control over the width of the bead, a modular die for applying adhesives, such as disclosed in U.S. Pat. No. 5,728,219 ('219), incorporated herein by reference, has been developed including interchangeable die bodies that include an internal valve for controlling the flow of polymer therethrough. Although the modular dies disclosed in '219 do provide increased flexibility over fixed die systems, it would be desirable to provide an adhesive dispensing unit with modular sections having gang actuated dispensing nozzles as well as modular sections where each dispensing nozzle operates individually. This dual modular section approach would provide maximum efficiency and variability of the adhesive dispensing unit.
In addition, there is an increasingly popular form of adhesive known as fast or rapid moisture cured adhesives. Such an adhesive may have a polyurethane base as is disclosed in U.S. Pat. No. 5,965,662, herein incorporated by reference. This type of adhesive provides a strong bond and has been found suitable for numerous applications including preformed structural assemblies. When these adhesives are dispensed, exposure to moisture in the air or to added moisture sprayed or otherwise applied to the adhesives, cause them to cure within minutes or even less.
One problem, though, with these rapid curing adhesives is that many standard or known adhesive applicators are not suitable. As exposure to air and moisture cures the adhesive within a rapid time, nozzle orifices can become clogged or valve stems may be adhered shut such that the unit will no longer function.
Due to the problem of dispensing highly reactive adhesives, a syringe-type adhesive applicator has been developed as disclosed in U.S. Pat. No. 5,016,784, incorporated herein by reference, which utilizes a non-stick polymeric seal and a hydrocarbon grease disposed between the seal and adhesive to provide a moisture impervious environment for the adhesive. The drawback to this syringe-type applicator is that it is designed primarily for low volume usage. As the syringe contains a fixed and limited amount of adhesive, it is not readily adaptable to an assembly line type application having continuous feed capabilities. Furthermore, on the opposite end of the nonstick polymeric seal is the dispensing nozzle, which is merely covered with a standard end cap. As such, after dispensing adhesive, the adhesive remaining in the nozzle area and around the cap may have been exposed to moisture and may solidify thereby clogging said nozzle.
One commercially available unit from BSI does provide a system that is intended for delivering multiple beads of rapid curing adhesive in a high volume application. This system includes a manifold having an inlet for the adhesive, an inner passageway in the manifold, and multiple nozzle ports connected with the passageway for dispensing the adhesive on a substrate. To preclude the nozzle orifices from clogging when the adhesive flow has been terminated, the nozzle tips are immersed in an oil bath. This allows the adhesive at the end of the nozzles, which has been exposed to the atmosphere, to drain into the oil and precludes any moisture or air from entering into the nozzle. One problem with this system is that when the nozzles are removed from the oil to continue dispensing adhesive, oil is pulled along and contaminates the initial portion of the bead. In addition, if frequent stops and starts are necessary, operators are reluctant to dip the nozzles into the oil as required due to the continual mess and contamination that results therefrom. Of course, if the nozzles are not dipped in the oil when the adhesive flow is turned off, then moisture will cure the adhesive in the nozzle orifice causing the unit to malfunction.
It is therefor an object of the invention to provide an adhesive dispensing unit that is suitable for an industrial high volume application and is capable of dispensing a highly reactive moisture cured adhesive such that the dispensing nozzles will not become clogged and without the necessity of immersing the nozzles in an oil bath.
It is another object of the invention to provide an adhesive dispensing unit having a modular design with manifolds having synchronously actuated adhesive dispensing orifices. It is also an object of the invention to provide other manifolds having individually actuated adhesive dispensing orifices, which can be individually controlled so as to provide optimum variability to the number and placement of adhesive beads.